very good questions!
- thicker walls means less capacity - 2mm less means half liter of capacity!
- I have to find how expencive would be the mould to shape the Al sheet - I am afraid of the fixed costs

Can they leave the mold thicker on the bottom and say, 1/4 of the way up the sides, then transition it to a thinner mold for the remainder of the sides and the top? That gives you the best of both worlds (thick bottom for abrasion resistance and thinner sides/top for additional capacity) without having to incorporate additional materials.